Separation systems, elements, and methods for separation utilizing stacked membranes and spacers

CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No. 16/584,714, filed Sep. 26, 2019, now U.S. Pat. No. 11,090,611, which is a divisional of U.S. patent application Ser. No. 15/470,757, filed Mar. 27, 2017, now U.S. Pat. No. 10,464,023, which is a divisional of U.S. patent application Ser. No. 14/137,903, filed Dec. 20, 2013, now U.S. Pat. No. 9,636,635, which claims the filing benefit of U.S. Provisional Application No. 61/745,300, filed Dec. 21, 2012. These applications are incorporated by reference herein in their entirety and for all purposes.

GOVERNMENT SPONSORSHIP

This invention was made with Government support under contract number W911NF-09-C-0079 awarded by the Department of Defense. The Government has certain rights in this invention.

TECHNICAL FIELD

Examples described herein relate to separation systems, elements, and methods which may be used for forward osmosis (FO), pressure retarded osmosis (PRO), or generally any separation process.

BACKGROUND

Membranes may be used to perform osmosis, which generally occurs when two solutions of differing concentration are placed on opposite sides of a permeable or semi-permeable membrane. The osmotic pressure difference between the two solutions drives the permeation of water across the membrane from the dilute solution to the concentrated solution, while the selective property of the membrane retains the solutes in their respective solution.

Plate and frame separation elements may generally include a plate and frame for enclosing a stack or array of membrane plate assemblies. Plate and frame separation elements may include a combination of a flat sheet membrane, a draw channel spacer, a flat sheet membrane, and feed channel spacer.

SUMMARY

Examples of separation systems, membrane plate assemblies, spacer plates, and methods are described herein. An example separation system may include a plurality of membrane plate assemblies. Each of the membrane plate assemblies may include a spacer plate having a spacing region. The spacer plate may at least partially define a first opening and a second opening. The spacer plate may include a first surface having a first bonding area and an opposing second surface having a second bonding area. The membrane plate assemblies may each include a first membrane bonded to the first surface at the first bonding area. The membrane plate assemblies may each includes second membrane bonded to the second surface at the second bonding area. The membrane plate assemblies may form a stack, with adjacent membrane plate assemblies in the stack having alternating orientations. The first surface and the second surface may have a staggered position with respect to one another. The first opening of the spacer plate may be in fluid communication with a region between the first and second membranes defining a first flow path. The separation system may further include support plates coupled to hold the membrane elements in a stack, wherein at least one of the support plates defines at least one fluid port.

In some examples, the spacing region may include a sheet comprising protrusions, cavities, textures, or combinations thereof on both sides, wherein the protrusions, cavities, textures, or combinations thereof are in contact with the first membrane and the second membrane, defining a flow path across the spacing region.

In some examples, the spacing region comprises an inner membrane assembly, wherein the inner membrane assembly comprises a third membrane on a first side of the spacer plate, a fourth membrane on a second side of the spacer plate.

In some examples, the separation system may further include a spacer sheet between at least two adjacent membrane surfaces.

In some examples, the separation system may further include a spacer sheet bonded to the first surface at the first bonding area and positioned on a side of the first membrane opposite the spacer plate, wherein the side of the spacer sheet opposite to the first membrane of the first membrane plate assembly is in contact with the side of the second membrane of a second membrane plate assembly opposite to the spacer plate of the second membrane plate assembly.

In some examples, the second opening is in fluid communication with a region between adjacent membrane plate assemblies in the stack defining a second flow path.

In some examples, the second opening is in fluid communication with a region between adjacent membrane plate assemblies in the stack and the third and fourth membranes defining a second flow path, and wherein the first opening is in fluid communication with regions between the first and third membranes and the second and fourth membranes.

In some examples, the first flow path is configured to facilitate flow of a fluid in a first direction in the regions between the first and third membranes and the second and fourth membranes and the second flow path is configured to facilitate flow of a fluid in a second direction in the region between the third and fourth membranes and between adjacent membrane plate assemblies in the stack defining a second flow path wherein the first and second directions are orthogonal.

In some examples, the at least one fluid port is in communication with the first opening of at least one membrane plate assembly and another fluid port is in communication with the second opening of at least one membrane plate assembly.

In some examples, the first and second openings are located on different edges of the spacer plate.

In some examples, the first flow path is configured to facilitate flow of a fluid in a first direction in the region between the first and second membranes and the second flow path is configured to facilitate flow of a fluid in a second direction in the regions between adjacent plate assemblies, wherein the first and second directions are orthogonal.

In some examples, the first opening of each spacer plate is configured to define any of a parallel, a series, or a series of parallel flow paths for the first fluid.

In some examples, the second opening of each spacer plate is configured to define any of a parallel, a series, or a series of parallel flow paths for the second fluid.

In some examples, the first opening of each spacer plate is coupled to one or more of the fluid ports of one or more support plates.

In some examples, the second opening of each spacer plate is coupled to one or more of the fluid ports of one or more support plates.

In some examples, the separation system is immersed in a first fluid, and each of the first openings are exposed to the first fluid.

In some examples, another fluid port is coupled to the second openings and is configured to provide a second fluid.

In some examples, each of the spacer plates is formed from an injection molded plastic.

In some examples, any of the first membranes or the second membranes are forward osmosis membranes.

In some examples, any of the first membranes or the second membranes comprise cellulose acetate, a thin film composite, polyamide, aramid, poly(vinylidene fluoride), or polypropylene.

In some examples, the membrane plate assemblies further comprise interconnects configured to define a parallel flow path or a series flow path.

An example method includes transporting a first fluid in a first direction in regions between certain ones of a plurality of membranes. An example method may further include transporting a second fluid in a second direction in other regions between other ones of the plurality of membranes. The first and second fluids may each comprise solutes, and the concentration of a solute may be higher in the first fluid such that the concentration of a solute in the second fluid is increased at least in part by fluid transport across the membranes. The first and second directions may be perpendicular directions.

In some examples, at least pairs of the certain ones of the plurality of membranes are bonded to respective spacer plates to form the regions and the respective spacer plates are stacked such that the bonded regions of the certain ones of the plurality of membranes are staggered in relation to one another.

In some examples, the regions between certain ones of the plurality of membranes are configured to define any of a parallel, a series, or a series of parallel flow paths of the first fluid.

In some examples, the regions between other ones of the plurality of membranes are configured to define any of a parallel, a series, or a series of parallel flow paths of the second fluid.

In some examples, at least pairs of the plurality of membranes are bonded to respective spacer plates, and the spacer plates are formed from an injection molded plastic.

In some examples, the membranes comprise cellulose acetate, a thin film composite, polyamide, aramid, poly(vinylidene fluoride), polypropylene, or combinations thereof.

In some examples, methods further include introducing air bubbles into any of the regions.

In some examples, methods further include transporting the first fluid or the second fluid in a parallel flow path to each of the regions between the certain ones of the plurality of membranes and transporting the other of the first fluid or the second fluid in a series flow path to each of the regions between the other ones of the plurality of membranes.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. <b>1</b></figref> is an illustration depicting perpendicular flow paths of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>2</b></figref> is a top down view of a spacer plate of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>3</b>A</figref> is a cross-sectional view of a spacer plate of a separation system along a first axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>3</b>B</figref> is a cross-sectional view of a spacer plate of a separation system along a second axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>4</b></figref> is an isometric view of a membrane plate assembly of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>5</b></figref> is an isometric view of multiple membrane plate assemblies arranged in a stack, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>6</b></figref> is an isometric view of the multiple membrane plate assemblies of <figref idref="DRAWINGS">FIG. <b>5</b></figref> showing bonding between each membrane plate assembly, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>7</b></figref> is an isometric view of the multiple membrane plate assembly of <figref idref="DRAWINGS">FIG. <b>5</b></figref> showing a channel provided by stacking the membrane plate assembly, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>8</b></figref> is a broken cross-sectional view of a separation system along a first axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>9</b></figref> is a broken cross-sectional view of a separation system along a second axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>10</b></figref> is a top down view of a spacer plate of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>11</b>A</figref> is a cross-sectional view of a spacer plate of a separation system along a first axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>11</b>B</figref> is a cross-sectional view of a spacer plate of a separation system along a second axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>12</b></figref> is an isometric view of a membrane plate assembly of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>13</b></figref> is a cross-sectional view of a membrane plate assembly of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>14</b></figref> is a sectional view of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>15</b></figref> is the sectional view of <figref idref="DRAWINGS">FIG. <b>14</b></figref> showing bonding between multiple membrane plate assemblies of the separation system along a first axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>16</b></figref> is the sectional view of <figref idref="DRAWINGS">FIG. <b>14</b></figref> showing bonding between multiple membrane plate assemblies of the separation system along a second axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>17</b></figref> is a cross-sectional view of a separation system along a first axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>18</b></figref> is a cross-sectional view of a separation system along a second axis, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>19</b></figref> is an isometric view of a separation system showing flow paths within the separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>20</b></figref> is an isometric view of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>21</b>A</figref> is cross-sectional view of a separation system stacked in parallel, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>21</b>B</figref> is a cross-sectional view of a separation system stacked in series, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>21</b>C</figref> is a cross-sectional view of a separation system stacked in a combination of series and parallel, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>22</b>A</figref> is an isometric view of a nipple of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>22</b>B</figref> is a top down view of a closed nipple, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>22</b>C</figref> is a cross-sectional view of a closed nipple, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>22</b>D</figref> is a top down view of an open nipple, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>22</b>E</figref> is a cross-sectional view of an open nipple, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>23</b></figref> is an isometric view of a separation system, according to some embodiments.

<figref idref="DRAWINGS">FIG. <b>24</b></figref> is an isometric view of a skid of membrane elements, according to some embodiments.

DETAILED DESCRIPTION

Certain details are set forth below to provide a sufficient understanding of embodiments of the invention. However, it will be clear to one skilled in the art that embodiments of the invention may be practiced without various of these particular details. In some instances, well-known chemical structures, chemical components, molecules, materials, manufacturing components, control systems, electronic components, timing protocols, and software operations have not been shown in detail in order to avoid unnecessarily obscuring the described embodiments of the invention.

Disclosed herein are example embodiments of systems, apparatuses and methods for forward osmosis (FO), pressure retarded osmosis (PRO), membrane distillation (MD), heat exchange membranes, evaporator membranes, contact membranes, condenser membranes, and absorber membranes, or generally any separation process. Examples include plate and frame separation elements adapted for use in four port separation where two flow paths may be used. Plate and frame separation elements may achieve low cost, high packing-density and high yield packaging. Four port separation is generally used herein to refer to separation involving two separate flow paths such that not all permeate passing through the membrane contributes to an exiting stream. Instead, a first fluid stream may be provided along a first fluid path and a second fluid stream may be provided along a second fluid path. The term four port separation is not intended to limit the number of ports which may be found on any particular element or separation system, although in some examples four ports may in fact be used.

<figref idref="DRAWINGS">FIG. <b>1</b></figref> is an illustration depicting perpendicular flow paths of a separation system, according to some embodiments. Example membrane elements described herein may utilize stacked membrane layers. Membranes, e.g. membrane <b>113</b> may be separated from other membranes by a flow spacer. A fluid flow path may enter in one or more points on one side of the membrane stack and may exit in one or more points on a separate side of the stack. Separation may be maintained between fluid flows on opposite sides of a membrane. This may be achieved in some examples without the need for a glue-line in the middle of two membrane layers (e.g. an envelope), resulting in an improved flow path in some examples. The one or more openings may be provided along a substantial portion of the edges of the membrane plate assemblies. Thus, the one or more openings may be the same width as the flow path, thereby facilitating a uniform velocity across the membrane plate assemblies in the stack.

By providing for perpendicular flow—e.g., a draw fluid flowing in a first direction <b>112</b> parallel to the plane of one side of a membrane and a feed fluid flowing in a second direction <b>111</b>, generally perpendicular to the first direction <b>112</b> on another side of the membrane—generally the entire membrane surface may be involved in fluid transfer (e.g. forward osmosis). Orthogonal flow may allow inlet and outlet manifolds to encompass the entire width of the flow path, leading to more uniformly distributed flows. This may avoid ‘dead zones’ associated with other fluid flow arrangements where the draw and feed fluids may not have uniform flow on either side of the entire membrane surface. Other fluid flow arrangements may also have higher head loss, resulting in lower performance of the separation system. The advantage of orthogonal flow may be provided for a ratio of the first fluid flow length to the second fluid flow length between 2:1 and 1:2 in some examples. Generally, orthogonal or perpendicular flow may refer to at least two flows oriented substantially 90 degrees with respect to one another such that an area of the membrane having different fluids on opposite sides may be maximized Several embodiments of a flow path for a separation system may be used. In some examples, the fluid flow path and associated components flowing between two membrane layers (e.g. inside a membrane envelope) may be a draw fluid, and the fluid flow path and associated components on an opposite side of the two membrane layers (e.g. outside the membrane envelope) may be a feed fluid. It will be understood that in some examples the opposite may be the case. Fluid flow paths may be provided over rectangular or square membrane layers where the draw fluid flow path enters along one edge, flows through the region between membranes to another (e.g. opposite) edge, as will be described below. It will be understood that membranes may be in other shapes, for example 5-sided, 6-sided, 8-sided, or circular shapes. The feed flow path <b>111</b> may be separated from the draw flow path <b>112</b> and can be co-current, counter-current, orthogonal-current or anything in between. Separated flow paths generally refer herein to flow paths which do not allow for fluid flow between the two paths (e.g. fluidically isolated paths), although in some examples some amount of mixing flows may occur that is not significant to the overall separation being performed. In some examples, the flows may separate the membranes of a stack, preventing or reducing the occurrence of the membranes clinging to one another. Both feed flow paths <b>111</b> and draw flow paths <b>112</b> within the separation system may be configured independently of one another in parallel, series or a combination of parallel and series. At the membrane surface, the draw and feed flow paths may be in cross flow, with velocities with respect to the membrane surface orthogonal to one another.

<figref idref="DRAWINGS">FIG. <b>2</b></figref> is a top down view of a spacer plate <b>100</b> of a separation system, according to some embodiments. The spacer plate <b>100</b> may include a spacing region. In some examples, the spacing region may include by a separating sheet <b>108</b>. In some examples, the spacing region may include an inner membrane assembly, as will be described below. The separating sheet <b>108</b> may be formed from an injection molded plastic, a woven material, or any sufficiently flat material that maintains the flow path inside the region between two membranes (e.g. inside an envelope). The separating sheet <b>108</b> may include features <b>109</b> on one or both sides. The features <b>109</b> may include protrusions, cavities, textures, or combinations thereof. The features <b>109</b> may be in contact with an upper membrane and/or a lower membrane in a flow path across the spacing region, as will be described below. The features <b>109</b> may create turbulence in the flow path across the spacing region Although the spacer plate <b>100</b> depicted is square, it will be understood that other geometries may be used in other examples, including geometries having three, four, five, six, or more sides or being round.

The spacer plate <b>100</b> may include one or more openings to facilitate fluid flow through or across the separation system. The one or more openings may assist in defining flow paths within the separation system. The fluid flow paths may be in parallel, series or a combination of parallel and series between adjacent membrane assemblies in a stacked system. With fluid flow paths in parallel, each membrane plate assembly may share a common opening and the fluid flow may be divided among the membrane plate assemblies. This may achieve a shortest possible flow path and lowest head losses. With fluid flow paths in series (e.g. serpentine), each membrane plate assembly may encompass the entire fluid flow rate. This may generally achieve the highest possible fluid velocity. Two separate fluid flow paths may be provided in this manner to facilitate the flow of two different fluids, for example a draw fluid and a feed fluid. In some examples, the two separate fluid flow paths may be provided with different combinations of series and parallel fluid flow paths. In some examples, the two separate fluid flow paths may be orthogonal to one another.

In some examples, the one or more openings may include an inlet opening and an outlet opening for a first fluid, for example a draw fluid. More than one inlet or outlet opening may be provided for the first fluid. In some examples, the inlet opening and the outlet opening may be on the opposite edges of the spacer plate <b>100</b> so as to facilitate flow of the first fluid in a first direction across the spacer plate. The inlet opening and the outlet opening may be in fluid communication with regions between the membrane plate assemblies of the separation system. In some examples, the spacer plate <b>100</b> may be in a first orientation, and the inlet opening may be opening <b>102</b> and the outlet opening may be opening <b>104</b>. In some examples, the spacer plate may be in a second orientation, and the inlet opening may be opening <b>104</b> and the outlet opening may be opening <b>102</b>. In some examples, the second orientation may be a 180° rotation about a third axis through the thickness of the spacer plate <b>100</b> (e.g., in plane) from the first orientation. In some examples, elements described herein may include a stack of membrane plate assemblies, with adjacent membrane plate assemblies in the stack having alternating orientations. In some examples the membranes bonded to the spacer plate <b>100</b> may have a staggered position with respect to one another. For example, the locations at which membranes are bonded to opposite sides of the spacer plate may not be the same (e.g. not on directly opposite locations on the spacer plate). In some examples, the location at which the membrane is bonded to the spacer plate is off-center such that when adjacent spacer plates are placed in different orientations in a stack (e.g. rotated 180 degrees with respect to one another), adjacent membranes in the stack may be staggered relative to one another. In this manner, flow paths may be defined by a combination of adjacent membrane plate assemblies, while allowing the spacer plates to be formed without the need for trapped features (e.g. the spacer plates may be injection molded). Although some examples described herein may refer to certain features, such as opening <b>102</b>, as an inlet opening and may refer to other features, such as opening <b>104</b>, as an outlet opening, it is to be understood that the openings on spacer plates and other flow paths described herein, such as opening <b>102</b> and opening <b>104</b>, may be either an inlet or an outlet depending on the orientation of the spacer plate or configuration of the flow path.

In some examples, the inlet opening, for example opening <b>102</b>, may be in fluid communication with the regions between the membrane plate assemblies by a first conduit, for example conduit <b>105</b>, that transports the first fluid to a second conduit, for example conduit <b>106</b>, that leads into the flow path across the spacing region <b>108</b>. So, for example, the opening <b>102</b> may form a fluid manifold when in a stack with multiple spacer places. The opening <b>102</b> may be in fluid communication with openings <b>105</b> and <b>106</b> which may allow fluid from the manifold region to pass under a portion of the spacer plate and enter, at opening <b>106</b>, a region between the spacer plate and membranes bonded to the spacer plate. After traveling across the spacing region, the first fluid may exit the spacer plate <b>100</b> through a third conduit, for example conduit <b>107</b>, that may be in fluid communication with the outlet opening, for example <b>104</b>. In some examples, the inlet opening and/or the outlet opening may be in fluid communication with one or more fluid ports, as will be described below. Similarly, the one or more openings may include an inlet opening, for example opening <b>101</b>, and an outlet opening, for example opening <b>103</b>, for a second fluid, for example a draw fluid. The inlet opening and outlet opening for the second fluid may be on different edges with respect to the inlet opening and outlet opening for the first fluid, and opposite with respect to one another. The openings <b>101</b> and <b>103</b> may form another conduit when stacked with other spacer plates, and may be in fluidic communication with regions between the adjacent membrane plate assemblies in the stack. For example, fluid entering the opening <b>101</b> (or <b>103</b>) may be able to pass between an upper membrane of the spacer plate <b>100</b> and a lower membrane of a spacer plate stacked above the spacer plate <b>100</b>. Fluid entering the opening <b>101</b> (or <b>103</b>) may traverse the region between spacer plates in the direction from <b>101</b> to <b>103</b> (or vice versa). This arrangement may facilitate a flow path for the second fluid that is orthogonal to the flow path for the first fluid.

Accordingly, examples of spacer plates described herein, including the spacer plate <b>100</b> of <figref idref="DRAWINGS">FIG. <b>2</b></figref> may include a first opening which is in fluid communication with a region between membranes bonded to the spacer plate. Example spacer plates may further include a second opening which may be in fluid communication with a region between adjacent plate assemblies when the plate assemblies are stacked.

In some examples, the one or more fluid ports may be fitted with interconnects to define a fluid connection between an upper and lower membrane element. In some examples, the interconnects may include nipples <b>2800</b> that may direct a fluid in a desired manner. As shown in <figref idref="DRAWINGS">FIG. <b>22</b></figref>, a nipple <b>2800</b> may be shaped to fit within a fluid port of the membrane element. The nipples <b>2800</b> may be coupled to the membrane elements using one or more sealing elements <b>2803</b>, for example O-rings. In some examples, there may be one or more sealing elements <b>2803</b> coupled to both an upper membrane element and a lower membrane element. A closed interconnect, for example closed nipple <b>2802</b> shown in <figref idref="DRAWINGS">FIGS. <b>22</b>B and <b>22</b>C</figref>, may block the opening separating a first membrane element from a second membrane element such that fluid cannot pass through from the first membrane element to the second membrane element. An open interconnect <b>2801</b>, for example open nipple <b>2801</b> shown in <figref idref="DRAWINGS">FIGS. <b>22</b>A, <b>22</b></figref><i>b</i>, and <b>22</b>C, may include a channel that allows for fluid communication through the opening separating a first membrane element from a second membrane element such that fluid may pass through from the first membrane element to the second membrane element. By connecting two or more elements in parallel, these interconnects may be used to configure the elements in parallel (<figref idref="DRAWINGS">FIG. <b>21</b>A</figref>), series (<figref idref="DRAWINGS">FIG. <b>21</b>B</figref>) or a combination of series and parallel (<figref idref="DRAWINGS">FIG. <b>21</b>C</figref>). The first flow path and the second flow path may be configured independently. In some examples the first flow path may be configured in parallel while the second flow path is configured in series. In this manner, a series flow, a parallel flow, or combinations thereof may be established between a stack of membrane elements.

During osmotic flow, membrane flux may be significantly reduced by concentration polarization (CP). Examples of separation systems disclosed herein may increase membrane flux by reducing concentration polarization. Membrane flux is generally proportional to the effective osmotic driving force. The osmotic driving force may be dissipated by CP, for example internal CP or external CP. Internal CP may be a function of a support layer of the membrane and the diffusion of the draw solute. The internal CP generally remains relatively constant with respect to the spacer plate geometry. External CP may exist within a boundary layer outside of the membrane thickness. External CP may be mitigated through adequate mixing in some examples.

Reduced CP may be achieved by using a spacer plate formed of injection molded plastic parts or stamped out of another material. This may allow for flexibility in spacer plate geometry as many shapes and surface textures can be molded with no or minimal increase to part cost. In this manner, the fabrication of an optimized spacer plate surface may be achieved with no or limited increase to part cost. An optimized spacer plate may advantageously mitigate external CP by increasing draw fluid turnover while maintaining a low head loss. This may reduce the amount of dilutive external CP, thereby increasing the effective osmotic driving force.

<figref idref="DRAWINGS">FIG. <b>3</b>A</figref> is a cross-sectional view of a spacer plate <b>100</b> of a separation system along a first axis, according to some embodiments. <figref idref="DRAWINGS">FIG. <b>3</b>B</figref> is a cross-sectional view of a spacer plate of a separation system along a second axis, according to some embodiments. The spacer plate <b>100</b> may include a first surface having one or more bonding areas. The bonding areas may be generally along the perimeter of the spacer plate <b>100</b>. In some examples, the bonding areas may be where an element of the separation system, for example a membrane or another spacer plate <b>100</b>, may be coupled to the spacer plate <b>100</b>. The element of the separation system may be coupled to the spacer plate <b>100</b> using an adhesive (e.g. pressure sensitive adhesive), by welding (e.g., thermal, solvent, or ultrasonic weld), a glued line, a fold in material, and/or any other known mechanism. The coupling may provide a fluidic seal. In some examples, a first bonding area of the first surface of the spacer plate <b>100</b> may include surfaces <b>210</b>, <b>212</b>, <b>214</b> and <b>216</b>. In some examples, a second bonding area of the first surface of the spacer plate <b>100</b> may include surfaces <b>220</b> and <b>233</b>, and may be staggered (e.g., asymmetrically arranged) about the second axis. The first and second bonding areas may be used to couple a first spacer plate <b>100</b> and a second spacer plate <b>100</b>. The spacer plate <b>100</b> may also include bonding areas for coupling the spacer plate <b>100</b> with a membrane <b>302</b>. These bonding areas may include surfaces <b>222</b> and <b>231</b>, which may be staggered about the second axis, and surfaces <b>234</b> and <b>236</b>, which may be symmetrical about the first axis.

The spacer plate <b>100</b> may include a second surface having similar bonding areas as the bonding areas on the first surface. The second surface may be located on an opposite side of the spacer plate <b>100</b> relative to the first surface. The second surface of a first spacer plate <b>100</b> may bond to the first surface of a second spacer plate <b>100</b>, as will be described below. In some examples, a first bonding area of the second surface of the spacer plate <b>100</b> may include surfaces <b>211</b>, <b>213</b>, <b>215</b> and <b>217</b>. In some examples, a second bonding area of the second surface of the spacer plate <b>100</b> may include surfaces <b>219</b> and <b>230</b>. The spacer plate <b>100</b> may also include bonding areas for coupling the spacer plate <b>100</b> with a membrane <b>303</b>. These bonding areas may include surfaces <b>219</b> and <b>230</b>, which may be staggered about the second axis, and surfaces <b>235</b> and <b>237</b>, which may be symmetrical about the first axis.

<figref idref="DRAWINGS">FIG. <b>4</b></figref> is an isometric view of a membrane plate assembly of a separation system, according to some embodiments. A membrane plate assembly may include a spacer plate <b>100</b>, a first membrane <b>302</b> (also referred to herein an “upper membrane”), a second membrane <b>303</b> (also referred to herein as a “lower membrane”), and a spacer sheet <b>304</b>. The first membrane <b>302</b> may be bonded to a first surface of the spacer plate <b>100</b> along the perimeter of the first membrane <b>302</b>. The second membrane <b>303</b> may be bonded to a second surface of the spacer plate <b>100</b> along the perimeter of the second membrane <b>303</b>. In some examples the first membrane may form a membrane to plate bond on surfaces <b>222</b>, <b>231</b>, <b>234</b>, and <b>236</b> around the entire perimeter of the membrane. The second membrane <b>303</b> may form a membrane to plate bond on surfaces <b>219</b>, <b>230</b>, <b>235</b> and <b>237</b> around the entire perimeter of the membrane. In some examples, the support side (backside) of the membranes may be bonded to the spacer plate <b>100</b>. In this manner, the membrane plate assembly may operate in a skin to feed mode (e.g., FO mode). In some examples, the skin side (frontside) of the membranes may be bonded to the spacer plate <b>100</b>. In this manner, the membrane plate assembly may operate in a skin to salt mode (e.g., PRO mode).

The first membrane <b>302</b> and the second membrane <b>303</b> may be formed from a variety of membrane materials including, but not limited to, cellulose acetate, polyacrylonitrile, meta-aramides (e.g., Nomex®) and/or para-aramids (e.g., Kevlar®), acrylate-modified poly(vinylidene fluoride), polyamide or thin film composite (TFC) with a polysulfone, polyamide, polyethersulfone, polyacrylonitrile, meta-aramides (e.g., Nomex®) and/or para-aramids (e.g., Kevlar®), acrylate-modified poly(vinylidene fluoride) polymer support layer, or any membrane suitable for forward osmosis. Different types of membranes may be used, for example reverse osmosis membranes, ultrafiltration membrane, membrane distillation membranes, or pressure retarded osmosis membranes.

The spacer sheet <b>304</b> may be formed from a material that supports a structured flow path between the two layers of membrane outside the envelope. The spacer sheet <b>304</b> may be implemented using a woven material, a molded plastic material, or any sufficiently flat material that maintains the flow path outside the envelope. The spacer sheet <b>304</b> may be positioned on a side of a membrane opposite the spacer plate <b>100</b>. The spacer sheet <b>304</b> may be coupled to the spacer plate <b>100</b> along its perimeter to a bonding area of the spacer plate <b>100</b> or a membrane. The coupling may be achieved using methods including, but not limited to, gluing, welding, mechanically fastening, or using an adhesive. In some examples, the spacer sheet <b>304</b> may be coupled to a first spacer plate <b>100</b> on surfaces <b>219</b> and <b>230</b> and a second spacer plate <b>100</b> on surfaces <b>222</b> and <b>231</b>. The spacer sheet <b>304</b> is optional and may not be included in all examples. When the spacer sheet <b>304</b> is absent, a void may be present in the region, allowing fluid flow.

Referring to <figref idref="DRAWINGS">FIG. <b>4</b></figref>, in some examples, a first fluid may enter fluid manifolds on the right or left-hand side of the Figure, and access the region between membranes <b>302</b> and <b>303</b> through, for example, the openings <b>105</b> and <b>107</b>. A second fluid may enter fluid manifolds shown on the upper or lower side of the Figure, and access regions between adjacent membrane plate assemblies (e.g. outside of the membranes <b>302</b> and <b>303</b>). The membranes <b>302</b> and <b>303</b> may be bonded to the plate across the width of the spacer plate shown in <figref idref="DRAWINGS">FIG. <b>4</b></figref>, such that fluid from the manifolds shown on the upper and lower edges of the spacer plate may be isolated from the region between the membranes <b>302</b> and <b>303</b>.

<figref idref="DRAWINGS">FIG. <b>5</b></figref> is an isometric view of multiple membrane plate assemblies arranged in a stack, according to some embodiments. Once stacked, the one or more openings of the spacer plates <b>100</b> may be arranged such that the inlets and outlets <b>101</b>, <b>102</b>, <b>103</b>, and <b>104</b> may align with one another to form a unified manifold. In some examples, the one or more openings aligned with one another may allow a fluid to be in fluid communication with multiple conduits of the spacer plates <b>100</b> of each of the membrane plate assemblies in the stack. In this manner, parallel flow may be achieved. In some examples, the openings of one of the spacer plates <b>100</b> may be blocked to force all of the fluid to pass through the conduits of that spacer plate <b>100</b>. In this manner, series flow may be achieved.

The spacer plates <b>100</b> may be stacked by coupling the plates together at their bonding areas, as described above. Perimeter plate to plate coupling may be achieved by joining surface <b>210</b> of a lower plate <b>1051</b> (See <figref idref="DRAWINGS">FIG. <b>8</b></figref>) to surface <b>213</b> of an upper plate <b>1050</b> and joining surface <b>212</b> of the lower plate <b>1051</b> to surface <b>211</b> of the upper plate <b>1050</b> and joining surface <b>214</b> of the lower plate <b>1051</b> to surface <b>217</b> of the upper plate <b>1050</b> and joining surface <b>216</b> of the lower plate <b>1051</b> to surface <b>215</b> of the upper plate <b>1050</b>. Joining the surfaces of the spacer plates <b>100</b> in this manner may result in an alternating arrangement of the spacer plates <b>100</b> in which each spacer plate <b>100</b> is rotated 180° in plane with respect to the spacer plate <b>100</b> adjacent to it. Note that the asymmetric design of the spacer plate <b>100</b> facilitates formation of flow paths using a single type of plate and without the need to have trapped features on the spacer plate <b>100</b> (e.g. the spacer plate <b>100</b> may be an injection molded part). Perimeter plate to plate coupling may separate the fluid flow paths from the outside world. In addition, internal plate to plate coupling may be achieved by joining surface <b>233</b> of the lower plate <b>1051</b> to surface <b>219</b> of the upper plate <b>1050</b> and surface <b>220</b> of the lower plate <b>1051</b> to surface <b>230</b> of the upper plate <b>1050</b>. Internal plate to plate coupling may separate the first fluid flow path and the second fluid flow path. Both the perimeter plate to plate coupling and the internal plate to plate coupling may include joining the plates along the entire width of the spacer plate <b>100</b>.

<figref idref="DRAWINGS">FIG. <b>6</b></figref> is an isometric view of the multiple membrane plate assemblies of <figref idref="DRAWINGS">FIG. <b>5</b></figref> showing bonding between each membrane plate assembly, according to some embodiments. The membrane plate assemblies in the stack may be in alternating orientations with respect to one another to allow the plate to be injection molded. A staggered second bonding area (internal seal separating draw from feed) may be achieved by an asymmetric arrangement of surfaces, as shown in <figref idref="DRAWINGS">FIGS. <b>3</b>A and <b>3</b>B</figref>. The asymmetric arrangement of surfaces of the spacer plate <b>100</b> may provide inner plate-to-plate bonding areas on both sides of the spacer plate <b>100</b> that are the same distance apart, but positioned at different points along the spacer plate <b>100</b>. In some examples, the spacer plates <b>100</b> may alternate in orientation to achieve the staggered membrane arrangement. For example, the distance between surface <b>220</b> and surface <b>233</b> may be the same as the distance as the distance between surface <b>219</b> and surface <b>230</b>. This may allow for surface <b>220</b> of a first plate to join with surface <b>230</b> of a second plate while surface <b>233</b> of the first plate joins with surface <b>219</b> of the second plate. As shown in <figref idref="DRAWINGS">FIG. <b>3</b>A</figref>, surface <b>220</b> may not be aligned with surface <b>219</b> and surface <b>233</b> may not be aligned with surface <b>230</b>. This offset may create a staggered arrangement. Continuing with the previous example, surface <b>219</b> of the first plate may join with surface <b>233</b> of a third plate and surface <b>230</b> of the first plate may join with surface <b>220</b> of the third plate. The second plate and third plate may be in alignment because the first plate may have been rotated 180° with respect to the second plate and the third plate may have rotated 180° about the third axis with respect to the first plate. By using an asymmetric arrangement of surfaces and alternating the membrane plate assemblies, it may be feasible to injection mold the spacer plates <b>100</b> out of one piece while maintaining a desired number of openings, for example four openings, and desired number of distinct flow paths, for example two distinct flow paths. In this manner, trapped features may be avoided, and only one type of plate may be required throughout the membrane element, and only one type of plate may be required throughout the membrane element, thereby enhancing manufacturing efficiency and packing density.

<figref idref="DRAWINGS">FIG. <b>7</b></figref> is an isometric view of the multiple membrane plate assemblies of <figref idref="DRAWINGS">FIG. <b>5</b></figref> showing a channel <b>900</b> provided by stacking the membrane plate assemblies, according to some embodiments. Channels <b>900</b> may be associated with a first fluid or a second fluid. Once stacked, an array of channels <b>900</b> for a first fluid may be on two sides of the stack and an array of channels <b>900</b> for a second fluid may be on another two sides of the stack. In some examples, the two sides that the array of channels <b>900</b> for each fluid is located are opposite to one another.

<figref idref="DRAWINGS">FIG. <b>8</b></figref> is a broken cross-sectional view of a separation system along a first axis, according to some embodiments. In some examples, a first fluid may enter from the inlet opening, for example the first inlet manifold <b>1054</b> formed by openings <b>102</b> and <b>104</b>, of the spacer plate <b>100</b> through an inlet channel <b>900</b> associated with the first fluid, and into a channel <b>1041</b> formed by surface <b>1232</b> of an upper spacer plate <b>1052</b> and surface <b>1218</b> of a lower spacer plate <b>1051</b>. The flow of the first fluid may split into two parts at point <b>238</b> shown in <figref idref="DRAWINGS">FIG. <b>3</b>A</figref>. In some examples, the two parts may be equal halves. The first fluid may then enter an upper channel <b>1042</b> and a lower channel <b>1043</b>. The upper channel <b>1042</b> may be formed by surface <b>229</b> of an upper plate <b>1050</b> and an upper membrane <b>302</b> of the upper plate <b>1050</b>. The lower channel <b>1043</b> may be formed by surface <b>221</b> of a lower plate <b>1051</b> and a lower membrane <b>303</b> of the lower plate <b>1051</b>. The upper channel <b>1042</b> may be coupled to an inner channel <b>1044</b> formed by the upper membrane <b>302</b> of the upper plate <b>1050</b> and the lower membrane <b>303</b> of the upper plate <b>1050</b>. The lower channel may be coupled to another inner channel <b>1045</b> formed by the upper membrane <b>302</b> of the lower plate <b>1051</b> and the lower membrane <b>303</b> of the lower plate <b>1051</b>.

The fluid traveling through the inner channel <b>1044</b> may then split into two parts at point <b>228</b> of the upper plate <b>1050</b>. A portion may enter an upper channel <b>1046</b> and a portion may enter a lower channel <b>1047</b>. The upper channel <b>1046</b> may be formed by surface <b>227</b> of the spacer plate <b>100</b> and the upper membrane <b>302</b> of the upper plate <b>1050</b>. The lower channel <b>1047</b> may be formed by surface <b>226</b> of the spacer plate <b>100</b> and the lower membrane <b>303</b> of the upper plate <b>1050</b>. The flows from both the upper channel <b>1046</b> and the lower channel <b>1047</b> may travel across the membrane plate assembly. At point <b>223</b> of the spacer plate <b>100</b>, the flows traveling through the upper channel <b>1046</b> and the lower channel <b>1047</b> may recombine and exit through an outlet channel <b>900</b> associated with the first fluid to the outlet opening, for example the first outlet manifold <b>1055</b> formed by opening <b>102</b> and <b>104</b>, of the spacer plate <b>100</b>.

<figref idref="DRAWINGS">FIG. <b>9</b></figref> is a broken cross-sectional view of a separation system along a second axis, according to some embodiments. A second fluid may enter from an inlet opening, for example the second inlet manifold <b>131</b> formed by opening <b>101</b> and <b>103</b>, of the spacer plate <b>100</b> through an inlet channel <b>900</b> associated with the second fluid. The second fluid may be transported into the spacer sheet <b>304</b> of a lower plate <b>1163</b> trapped in a channel formed by surface <b>234</b> of the lower plate <b>1163</b> and surface <b>237</b> of an upper plate <b>1162</b>. The second fluid may flow across the membrane plate assembly. The second fluid may exit through an outlet channel <b>900</b> associated with the second fluid and then exit through the outlet opening, for example the second outlet manifold <b>133</b> formed by opening <b>101</b> and <b>103</b>, of the spacer plate <b>100</b>.

<figref idref="DRAWINGS">FIG. <b>10</b></figref> is a top down view of a spacer plate <b>1200</b> of a separation system, according to some embodiments. It will be understood that spacer plate <b>1200</b> operates similarly to spacer plate <b>100</b> described above. Spacer plate <b>1200</b> may enhance the packing density of the membrane plate assemblies by minimizing dead space resulting from non-membrane materials. Instead of a separating sheet <b>108</b> in the spacing region, spacer plate <b>1200</b> may include an internal membrane assembly <b>1208</b> in its spacing region. Thus, dead volume resulting from the separating sheet <b>108</b> may be avoided. In addition to improving the packing density of the membrane plate assemblies, this arrangement may increase the membrane sheet area by increasing the overall dimensions of the spacer plate <b>1200</b>. It may be possible to increase the overall dimensions of the spacer plate <b>1200</b> while still satisfying minimum thickness and maximum area manufacturing requirements. The spacer plate <b>1200</b> may also reduce the plate cost per membrane area since the volume of material, for example plastic, that may be required to form the spacer plate <b>1200</b> may be reduced. The spacer plate <b>1200</b> may include no trapped features, which may allow it to be molded in a simple two part mold. Although the spacer plate <b>1200</b> depicted is square, it will be understood that other geometries may be used in other examples, including geometries having three, four, five, six, or more sides or being round.

The spacer plate <b>1200</b> may include an inlet opening, for example opening <b>1202</b>, and an outlet opening, for example opening <b>1204</b>, for a first fluid, for example a draw fluid. More than one inlet or outlet opening may be provided for the first fluid. In some examples, the inlet opening and the outlet opening may be on the opposite edges of the spacer plate <b>1200</b> so as to facilitate flow of the first fluid in a first direction across the spacer plate. The inlet opening and the outlet opening may be in fluid communication with regions between the membrane plate assemblies of the separation system. In some examples, the spacer plate <b>1200</b> may be in a first orientation, and the inlet opening may be opening <b>1202</b> and the outlet opening may be opening <b>1204</b>. In some examples, the spacer plate may be in a second orientation, and the inlet opening may be opening <b>1204</b> and the outlet opening may be opening <b>1202</b>. In some examples, the second orientation may be a 180° rotation of the spacer plate <b>1200</b> from the first orientation. Although some examples may show opening <b>1202</b> as an inlet opening and opening <b>1204</b> as an outlet opening or vice versa, it will be understood that opening <b>1202</b> and opening <b>1204</b> may be either an inlet or an outlet depending on the orientation of the spacer plate <b>1200</b>.

In some examples, the inlet opening may be in fluid communication with the regions between the membrane plate assemblies by a first conduit, for example conduit <b>1205</b>, that transports the first fluid to a second conduit, for example conduit <b>1206</b>, that leads into the flow path across the spacing region <b>1208</b>. After traveling across the spacing region, the first fluid may exit the spacer plate through a third conduit, for example conduit <b>1207</b>, that may be in fluid communication with the outlet opening. In some examples, the inlet opening and/or the outlet opening may be in fluid communication with one or more fluid ports, as will be described below.

In some examples the one or more openings may include an inlet opening, for example opening <b>1201</b>, and an outlet opening, for example opening <b>1203</b>, for a second fluid, for example a feed fluid. More than one inlet or outlet may be provided for the second fluid. In some examples, the inlet opening and the outlet opening may be on the opposite edges of the spacer plate <b>1200</b> so as to facilitate flow of the second fluid in a in an orthogonal direction with respect to the first fluid across the spacer plate <b>1200</b>. In some examples, the spacer plate <b>1200</b> may be in a first orientation, and the inlet opening may be opening <b>1202</b> and the outlet opening may be opening <b>1204</b>. In some examples, the spacer plate may be in a second orientation, and the inlet opening may be opening <b>1204</b> and the outlet opening may be opening <b>1202</b>. In some examples, the second orientation may be a 180° rotation of the spacer plate <b>1200</b> from the first orientation. Although some examples may show opening <b>1202</b> as an inlet opening and opening <b>1204</b> as an outlet opening or vice versa, it will be understood that opening <b>1202</b> and opening <b>1204</b> may be either an inlet or an outlet depending on the orientation of the spacer plate <b>1200</b>.

In some examples, the inlet opening may be in fluid communication with the regions outside of the regions between the membranes and the inner membrane assembly <b>1208</b> by a first conduit, for example conduit <b>1212</b>. The second fluid may exit the membrane plate assembly through a second conduit, for example conduit <b>1211</b>. In some examples, the inlet opening and/or the outlet opening may be in fluid communication with one or more fluid ports, as will be described below.

In some examples, the one or more openings may be fitted with interconnects to define a parallel flow path or a series flow path. The interconnects may block the opening such that fluid cannot pass through in order to facilitate a series flow. The interconnects may allow flow through an opening to the spacer plate below in order to facilitate a parallel flow. In this manner, a series flow, a parallel flow, or combinations thereof may be established between a stack of spacer plates. In some examples, the interconnects may include nipples that may direct a fluid in a desired manner.

<figref idref="DRAWINGS">FIG. <b>11</b>A</figref> is a cross-sectional view of a spacer plate <b>1200</b> of a separation system along a first axis, according to some embodiments. <figref idref="DRAWINGS">FIG. <b>11</b>B</figref> is a cross-sectional view of a spacer plate <b>1200</b> of a separation system along a second axis, according to some embodiments. The spacer plate <b>1200</b> may include a first surface having one or more bonding areas. The bonding areas may be generally along the perimeter of the spacer plate <b>1200</b>. In some examples, the bonding areas may be where an element of the separation system, for example a membrane or another spacer plate <b>1200</b>, may be coupled to the spacer plate <b>1200</b>. The element of the separation system may be coupled to the spacer plate <b>1200</b> using an adhesive (e.g. pressure sensitive adhesive), by welding (e.g., thermal or ultrasonic weld), a glued line, a fold in material, and/or any other known mechanism. The coupling may provide a fluidic seal. In some examples, a first bonding area of the first surface of the spacer plate <b>1200</b> may include surfaces <b>1320</b>, <b>1342</b>, <b>1350</b> and <b>1367</b>. In some examples, a second bonding area of the first surface of the spacer plate <b>1200</b> may include surfaces <b>1325</b> and <b>1340</b>, and may be staggered (e.g., asymmetrically arranged) about the second axis. The first and second bonding areas may be used to couple a first spacer plate <b>1200</b> and a second spacer plate <b>1200</b>.

The spacer plate <b>1200</b> may include a second surface having similar bonding areas to the first surface. The second surface may be located on an opposite side of the spacer plate <b>1200</b> relative to the first surface. The second surface of the first spacer plate <b>1200</b> may bond to the first surface of a second spacer plate <b>1200</b> as will be described below. In some examples, a first bonding area of the second surface of the spacer plate <b>1200</b> may include surfaces <b>1321</b>, <b>1343</b>, <b>1351</b> and <b>1368</b>. In some examples a second bonding area of a second surface of the spacer plate <b>1200</b> may include surfaces <b>1323</b> and <b>1337</b>, and may be staggered (asymmetrically arranged) about the second axis of spacer plate <b>1200</b>.

The spacer plate <b>1200</b> may also include bonding areas for coupling the spacer plate <b>1200</b> with a membrane <b>1403</b>. These bonding areas may include surfaces <b>1327</b> and <b>1338</b>, which may be staggered about the second axis, and surfaces <b>1356</b> and <b>1366</b>, which may be staggered about the first axis. The spacer plate <b>1200</b> may also include bonding areas for coupling the spacer plate <b>1200</b> with a membrane <b>1406</b>. These bonding areas may include surfaces <b>1329</b> and <b>1333</b>, which may be symmetrical about the second axis, and surfaces <b>1358</b> and <b>1364</b>, which may be staggered about the first axis. The spacer plate <b>1200</b> may also include bonding areas for coupling the spacer plate <b>1200</b> with a membrane <b>1408</b>. These bonding areas may include surfaces <b>1330</b> and <b>1334</b>, which may be symmetrical about the second axis, and surfaces <b>1355</b> and <b>1361</b>, which may be staggered about the first axis. The spacer plate <b>1200</b> may also include bonding areas for coupling the spacer plate <b>1200</b> with a membrane <b>1410</b>. These bonding areas may include surfaces <b>1323</b> and <b>1337</b>, which may be staggered about the second axis, and surfaces <b>1353</b> and <b>1363</b>, which may be staggered about the first axis.

<figref idref="DRAWINGS">FIG. <b>12</b></figref> is an isometric view of a membrane plate assembly of a separation system, according to some embodiments. The membrane plate assembly may include the spacer plate <b>1200</b>, a spacer sheet <b>1402</b> (also referred to herein as “first spacer sheet”), a first membrane <b>1403</b>, and a second membrane <b>1410</b>. The spacer sheet <b>1402</b> may be similar to the spacer sheet <b>304</b> described above. In addition, the first membrane <b>1403</b> (also referred to herein as “upper outer membrane”) and the second membrane <b>1410</b> (also referred to herein as “lower outer membrane”) may be similar to the first membrane <b>302</b> and the second membrane <b>303</b> described above. The membrane plate assembly may also include an inner membrane assembly <b>1208</b>. The inner membrane assembly may be a multi-layer assembly including a second spacer sheet <b>1407</b>, a third membrane <b>1406</b> (also referred to herein as “upper inner membrane”) on a first side of the second spacer sheet <b>1407</b>, a third spacer sheet <b>1405</b> on a side of the third membrane <b>1406</b> opposite the second spacer sheet <b>1407</b>, a fourth membrane <b>1408</b> (also referred to herein as “lower inner membrane) on a second side of the second spacer sheet <b>1407</b>, and a fourth spacer sheet <b>1409</b> on a side of the fourth membrane <b>1408</b> opposite the second spacer sheet <b>1407</b>. In some examples, the first membrane <b>1403</b>, the second membrane <b>1410</b>, the third membrane <b>1406</b> and the fourth membrane <b>1408</b> may be forward osmosis membranes.

<figref idref="DRAWINGS">FIG. <b>13</b></figref> is a cross-sectional view of a membrane plate assembly of a separation system, according to some embodiments. <figref idref="DRAWINGS">FIG. <b>13</b></figref> shows the relatively small amount of space occupied by the spacer plate <b>1200</b> and the relatively large amount of space occupied by the membranes and spacers. The high proportion of spacers and membranes relative to dead space from the spacer plate <b>1200</b> results in a higher packing density and a higher level of separation that may be carried out in a given amount of space.

The lower surface of the first spacer sheet <b>1402</b> may be in contact with the upper surface of an upper outer membrane <b>1403</b> of a lower plate <b>2184</b> (See <figref idref="DRAWINGS">FIG. <b>17</b></figref>). The upper surface of the first spacer sheet <b>1402</b> may be in contact with the lower surface of a lower outer membrane <b>1410</b> of an upper plate <b>2171</b>. The upper plate <b>2171</b> may separate the upper outer membrane <b>1403</b> from the lower outer membrane <b>1410</b>, and may provide a structured flow path between them. The lower surface of the third spacer sheet <b>1405</b> may be in contact with the upper surface of the upper inner membrane <b>1406</b>. The upper surface of the third spacer sheet <b>1405</b> may be in contact with the lower surface of the upper outer membrane <b>1403</b>. The third spacer sheet <b>1405</b> may separate the upper outer membrane <b>1403</b> from the upper inner membrane <b>1406</b>, and may provide a structured flow path between them. The lower surface of the second spacer sheet <b>1407</b> may be in contact with the upper surface of the lower inner membrane <b>1408</b>. The upper surface of the second spacer sheet <b>1407</b> may be in contact with the lower surface of the upper inner membrane <b>1406</b>. The second spacer sheet <b>1407</b> may separate the lower inner membrane <b>1408</b> from the upper inner membrane <b>1406</b>, and provide a structured flow path between them. The lower surface of a fourth spacer sheet <b>1409</b> may be in contact with the upper surface of the lower outer membrane <b>1410</b>. The upper surface of the fourth spacer sheet <b>1409</b> may be in contact with the lower surface of the lower inner membrane <b>1408</b>. The fourth spacer sheet <b>1409</b> may separate the lower outer membrane <b>1410</b> from the lower inner membrane <b>1408</b>, and provide a structure flow path between them.

<figref idref="DRAWINGS">FIG. <b>14</b></figref> is a sectional view of a separation system, according to some embodiments. Like <figref idref="DRAWINGS">FIG. <b>13</b></figref>, <figref idref="DRAWINGS">FIG. <b>14</b></figref> shows the relatively small amount of space occupied by the spacer plate <b>1200</b> and the relatively large amount of space occupied by the membranes and spacers. The membrane plate assemblies may be stacked, whereby one or more openings of the spacer plates <b>1200</b> may be arranged to be aligned with one another. Any number of membrane plate assemblies may be stacked to form an element, including 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 membrane plate assemblies, or more in other examples. Adjacent membrane plate assemblies in the stack may have having alternating orientations and may have membranes staggered in position with respect to one another, as shown in examples described herein. In some examples, the one or more openings aligned with one another may allow a fluid to be in fluid communication with multiple conduits of the spacer plates <b>1200</b> of each of the membrane plate assemblies in the stack. In this manner, parallel flow may be achieved. In some examples, the openings of one of the spacer plates <b>1200</b> may be blocked to force all of the fluid to pass through the conduits of that spacer plate <b>1200</b>. In this manner, series flow may be achieved.

The spacer plates <b>1200</b> may be stacked by coupling the plates together at their bonding areas, as described above. Perimeter plate to plate coupling may be achieved by joining surface <b>1320</b> of a lower plate <b>2184</b> (See <figref idref="DRAWINGS">FIG. <b>17</b></figref>) to surface <b>1343</b> of an upper plate <b>2171</b> and joining surface <b>1342</b> of the lower plate <b>2184</b> to surface <b>1321</b> of the upper plate <b>2171</b>. Joining the surfaces of the spacer plates <b>1200</b> in this manner may result in an alternating arrangement of the spacer plates <b>1200</b> in which each spacer plate <b>1200</b> is rotated 180° about a third axis with respect to the spacer plate <b>1200</b> adjacent to it. Perimeter plate to plate coupling may separate the fluid flow paths from the outside world. In addition, internal plate to plate coupling may be achieved by joining surface <b>1340</b> of the lower plate <b>2184</b> to surface <b>1323</b> of the upper plate <b>2171</b> and surface <b>1325</b> of the lower plate <b>2184</b> to surface <b>1337</b> of the upper plate <b>2171</b>. Internal plate to plate coupling may separate the first fluid flow path and the second fluid flow path. Both the perimeter plate to plate coupling and the internal plate to plate coupling may include joining the plates along the entire width of the spacer plate <b>1200</b>.

<figref idref="DRAWINGS">FIG. <b>15</b></figref> is the sectional view of <figref idref="DRAWINGS">FIG. <b>14</b></figref> showing bonding between multiple membrane plate assemblies of the separation system along a first axis, according to some embodiments. <figref idref="DRAWINGS">FIG. <b>16</b></figref> is the sectional view of <figref idref="DRAWINGS">FIG. <b>14</b></figref> showing bonding between multiple membrane plate assemblies of the separation system along a second axis, according to some embodiments. The membranes of the membrane plate assemblies in the stack may be staggered with respect to one another. It may be advantageous to stagger the membranes to improve packing efficiency and due to manufacturing considerations. Staggering may be achieved by an asymmetric arrangement of surfaces, as shown in <figref idref="DRAWINGS">FIGS. <b>11</b>A and <b>11</b>B</figref>. In some examples, the spacer plates <b>1200</b> may alternate in orientation to achieve the staggered arrangement. The asymmetric arrangement of surfaces of the spacer plate <b>1200</b> may provide inner plate-to-plate bonding areas on both sides of the spacer plate <b>1200</b> that are the same distance apart, but positioned at different points along the spacer plate <b>1200</b>. In some examples, the spacer plates <b>100</b> may alternate in orientation to achieve the staggered arrangement. For example, the distance between surface <b>1325</b> and surface <b>1340</b> may be the same as the distance as the distance between surface <b>1323</b> and surface <b>1337</b>. This may allow for surface <b>1325</b> of a first plate to join with surface <b>1337</b> of a second plate while surface <b>1340</b> of the first plate joins with surface <b>1323</b> of the second plate. As shown in <figref idref="DRAWINGS">FIG. <b>11</b>A</figref>, surface <b>1325</b> may not be aligned with surface <b>1323</b> and surface <b>1340</b> may not be aligned with surface <b>1337</b>. This offset may create a staggered arrangement. Continuing with the previous example, surface <b>1323</b> of the first plate may join with surface <b>1340</b> of a third plate and surface <b>1337</b> of the first plate may join with surface <b>1325</b> of the third plate. The second plate and third plate may be in alignment because the first plate may have been rotated 180° about a third axis with respect to the second plate and the third plate may have been rotated 180° about the third axis with respect to the first plate. By using an asymmetric arrangement of surfaces and staggering the membrane plate assemblies, it may be feasible to injection mold the spacer plates <b>1200</b> out of one piece while maintaining a desired number of openings, for example four openings, and desired number of distinct flow paths, for example two distinct flow paths. In this manner, trapped features may be avoided, thereby enhancing manufacturing efficiency and packing density.

The upper outer membrane <b>1403</b> may form a membrane to plate bond on surfaces <b>1327</b>, <b>1338</b>, <b>1356</b>, and <b>1366</b> of the spacer plate <b>1200</b>. The upper inner membrane <b>1406</b> may form a membrane to plate bond on surfaces <b>1329</b>, <b>1333</b>, <b>1358</b>, and <b>1364</b> of the spacer plate <b>1200</b>. The lower inner membrane <b>1408</b> may form a membrane to plate bon on surfaces <b>1330</b>, <b>1334</b>, <b>1355</b>, and <b>1361</b> of the spacer plate <b>1200</b>. The lower outer membrane <b>1410</b> may form a membrane to plate bond on surfaces <b>1323</b>, <b>1337</b>, <b>1353</b>, and <b>1363</b> of the spacer plate <b>1200</b>. The membrane to plate bond for the upper outer membrane <b>1403</b>, the upper inner membrane <b>1406</b>, the lower inner membrane <b>1408</b>, and the lower outer membrane <b>1410</b> may be provided around the entire perimeter of the membrane.

<figref idref="DRAWINGS">FIG. <b>17</b></figref> is a cross-sectional view of a separation system along a first axis, according to some embodiments. In some examples, a first fluid, for example a draw fluid, may enter the membrane plate assembly from the inlet opening, for example an inlet manifold <b>1231</b> formed by openings <b>1201</b> and <b>1203</b>, and travel through an inlet channel associated with the first fluid, and into a channel <b>2172</b> formed by surface <b>1339</b> of an upper place <b>2171</b> and surface <b>1322</b> of a lower plate <b>2184</b>. The fluid flow path may be split into two halves at point <b>1324</b>, whereby it enters an upper channel <b>2174</b> and a lower channel <b>2185</b>. The upper channel <b>2174</b> may be formed by surface <b>1336</b> of the upper plate <b>2171</b> and the upper outer membrane <b>1403</b> of the upper plate <b>2171</b>. The lower channel <b>2185</b> may be formed by surface <b>1326</b> of the lower plate <b>2184</b> and the lower outer membrane <b>1410</b> of the lower plate <b>2184</b>.

The upper channel <b>2174</b> may direct the first fluid to a channel <b>2175</b> formed by the upper outer membrane <b>1403</b> of the upper plate <b>2171</b> and the lower outer membrane <b>1410</b> of the upper plate <b>2171</b>. The lower channel <b>2185</b> may direct the first fluid to a channel <b>2186</b> formed by the upper outer membrane <b>1403</b> of the lower plate <b>2184</b> and the lower outer membrane <b>1410</b> of the lower plate <b>2184</b>. The channel <b>2175</b> may then split into two halves at point <b>1335</b> of the upper plate <b>2171</b>, whereby it may enter an upper channel <b>2176</b> or a lower channel <b>2177</b>. The upper channel <b>2176</b> may be formed by surface <b>1333</b> of the spacer plate <b>1200</b> and the upper outer membrane <b>1403</b> of the upper plate <b>2171</b>. The lower channel <b>2177</b> may be formed by surface <b>1334</b> of the spacer plate <b>1200</b> and the lower outer membrane <b>1410</b> of the upper plate <b>2171</b>.

The upper channel <b>2176</b> may direct the first fluid to a channel <b>2178</b>, which is formed by the upper outer membrane <b>1403</b> and the upper inner membrane <b>1406</b> of an upper plate <b>2171</b>, whereby the first fluid may travel through the third spacer sheet <b>1405</b>. The lower channel <b>2177</b> may direct the first fluid to a channel <b>2179</b>, which is formed by the lower outer membrane <b>1410</b> and the lower inner membrane <b>1408</b> of the upper plate <b>2171</b>, whereby the first fluid may travel through fourth spacer sheet <b>1409</b>. The flows through channel <b>2178</b> and channel <b>2179</b> may transport the first fluid across the spacer plate <b>1200</b> contacting the membranes. At point <b>1328</b> of the spacer plate <b>1200</b>, channel <b>2178</b> and channel <b>2179</b> recombine ad the first fluid may exit through the outlet opening <b>1203</b> following a similar path through the outlet channels. In some examples, the flow entering the outlet opening <b>1203</b> may interact with merging flows from the upper plate <b>2173</b>. The upper stream may not meet the lower stream <b>2186</b> until they have both reached outlet opening, for example outlet manifold <b>1233</b> formed by openings <b>1201</b> and <b>1203</b>.

<figref idref="DRAWINGS">FIG. <b>18</b></figref> is a cross-sectional view of a separation system along a second axis, according to some embodiments. In some examples, a second fluid, for example a feed fluid, may enter from the inlet opening, for example inlet manifold <b>1232</b> formed by openings <b>1202</b> and <b>1204</b>, through an inlet channel associated with the second fluid into channel <b>2202</b> formed by surface <b>1353</b> of an upper plate <b>2201</b> and surface <b>1366</b> of a center plate <b>2203</b>, and into channel <b>2204</b> formed by surface <b>1365</b> of a center plate <b>2203</b> and surface <b>1354</b> of a lower plate <b>2212</b>. Channel <b>2204</b> may split into three even paths: an upper flow path <b>2204</b>, a center flow path <b>2206</b>, and a lower flow path <b>2213</b>. The upper flow path <b>2205</b> may be formed by surface <b>1362</b> and the upper inner membrane <b>1406</b> of the center plate <b>2203</b>. The center flow path <b>2206</b> may be formed by surface <b>1363</b> of the center plate <b>2203</b> and surface <b>1356</b> of the lower plate <b>2212</b>. The lower flow path <b>2213</b> may be formed by surface <b>1326</b> and the lower inner membrane <b>1408</b> of the lower plate <b>2212</b>.

Channel <b>2202</b> may direct the second fluid into a channel formed by the lower outer membrane <b>1410</b> of the upper plate <b>2201</b> and the upper outer membrane <b>1403</b> of the center place <b>2203</b>. The second fluid may then flow through the first spacer sheet <b>1402</b> of the center plate <b>2203</b>. The upper flow path <b>2205</b> may lead to channel <b>2208</b>, which is formed by the upper inner membrane <b>1406</b> and the lower inner membrane <b>1408</b> of the center plate <b>2203</b>. Channel <b>2208</b> may direct the second fluid through the second spacer sheet <b>1407</b> of the center plate <b>2203</b>. Channel <b>2208</b> may then direct the second fluid to channel <b>2209</b>, which may be formed by surface <b>1357</b> and the lower inner membrane <b>1408</b> of the center plate <b>2203</b>. Channels <b>2207</b>, <b>2209</b> and <b>2210</b> may then combine in channel <b>2211</b>, and exit to the outlet opening, for example outlet manifold <b>1234</b> formed by openings <b>1202</b> and <b>1204</b>.

The center flow path <b>2206</b> may enter channel <b>2214</b> formed by the lower outer membrane <b>1410</b> of the center plate <b>2203</b> and the upper outer membrane <b>1403</b> of the lower plate <b>2212</b>. Channel <b>114</b> may direct the second fluid through the first spacer sheet <b>1402</b> of the lower plate <b>2212</b>. Channel <b>2214</b> may direct the second fluid to the outlet opening.

The lower flow path <b>2213</b> may enter channel <b>2215</b>, which may be formed by the upper inner membrane <b>1406</b> and the lower inner membrane <b>1408</b> of the lower plate <b>2212</b>. Channel <b>2215</b> may direct the second fluid through the second spacer sheet <b>1407</b> of the lower plate <b>2212</b>. Channels <b>2215</b>, <b>2216</b>, and <b>2217</b> may then combine n channel <b>2218</b>, and exit to the outlet opening.

<figref idref="DRAWINGS">FIG. <b>19</b></figref> is an isometric view of a separation system showing flow paths within the separation system, according to some embodiments. The one or more openings may direct a fluid from a first side of a membrane plate assembly to a second side of the membrane plate assembly. A flow path of the first fluid, for example a draw fluid, may be along a first axis. In some examples, the first side and the second side may be opposite edges of the spacer plate <b>100</b>. For example, a first fluid inlet flow path <b>2301</b> may direct a first fluid from outside the separation system to the first inlet manifold <b>1054</b> of the separation system, as described above. The first fluid may enter the membrane plate assembly through the inlet channel and flow along a first axis and out through first outlet manifold <b>1055</b> of the separation system. A first fluid outlet flow path <b>2302</b> may direct the first fluid exiting each spacer plate <b>100</b> out of the separation system.

A flow path of the second fluid, for example a feed fluid, may be along a second axis. In some examples, the second axis may be orthogonal to the first axis. In some examples, the second axis may be at a different angle with respect to the first axis. In some examples, the first side and the second side may be opposite edges of the spacer plate <b>100</b>. For example, a second fluid inlet flow path <b>2303</b> may direct a first fluid from outside the separation system to the second inlet manifold <b>131</b> of the separation system, as described above. The first fluid may enter the membrane plate assembly through the inlet channel and flow along a second axis and out through second outlet manifold <b>133</b> of the separation system. A second fluid outlet flow path <b>2304</b> may direct the second fluid exiting each spacer plate <b>100</b> out of the separation system.

In some examples, air bubbles may be introduced, flowing through the feed flow path, to reduce the propensity of membrane fouling in the separation system.

<figref idref="DRAWINGS">FIG. <b>20</b></figref> is an isometric view of a membrane element <b>2400</b>, according to some embodiments. Assembly of the membrane element <b>2400</b> may be completed by adhering a foot plate <b>2406</b> and a head plate <b>2405</b>. The head plate <b>2405</b> and foot plate <b>2406</b> may be sealed, for example, with a mechanical seal, adhesive seal or weld. The foot plate may seal the bottom of the membrane element <b>2400</b>. The head plate <b>2405</b> may provide a sealing surface for the one or more openings of the spacer plates and may supply plumbing options, for example fluid ports. The head plate <b>2405</b> may be positioned at the top of the membrane element <b>2400</b>, and may include one or more fluid ports coupled to the one or more openings. A first fluid port <b>2401</b> may be provided to receive a first fluid, for example a feed fluid, and transport it to a first inlet manifold <b>1054</b> of the separation system. A second fluid port <b>2402</b> may provide an outlet for first fluid that has passed through the membrane element <b>2400</b> and into the first outlet manifold <b>1055</b> of the separation system. In some examples, the second fluid port <b>2402</b> may be located on the foot plate <b>2406</b>. A third fluid port <b>2403</b> may be provided to receive a second fluid, for example a draw fluid, and transport it to a second inlet manifold <b>131</b> of the separation system A fourth fluid port <b>2404</b> may provide an outlet for second fluid that has passed through the membrane element <b>2400</b> and into the second outlet manifold <b>133</b> of the separation system. Other ports may also be present, or multiple ports used per inlet and outlet in some examples. <figref idref="DRAWINGS">FIG. <b>21</b>A</figref> is cross-sectional view of a membrane element <b>2400</b> stacked in parallel, according to some embodiments. Examples of separation systems described herein may maintain a flow path for four port elements while increasing packing density, increasing yields and decreasing head losses in some examples. This may result in a substantially lower head loss due to an improved flow path. In some examples multiple membrane elements <b>2400</b> may be coupled by aligning their fluid ports. A top plate first fluid port <b>2501</b> may direct a first fluid to a first fluid port <b>2401</b> of the head plate of a first membrane element <b>2400</b>. The first fluid may then pass through the first membrane element <b>2400</b>. The first fluid may then pass to a membrane element <b>2400</b> by exiting the first membrane element <b>2400</b> through a second fluid port <b>2402</b> located on the foot plate of the first membrane element <b>2400</b>. The second fluid port <b>2402</b> may be coupled to first fluid port <b>2401</b> of a second membrane element <b>2400</b> positioned beneath the first membrane element <b>2400</b>. Similarly, the first fluid may pass through a third membrane element <b>2400</b>. For a parallel configuration, all the first fluid ports <b>2401</b> and second fluid ports <b>2402</b> may be on a first side of each membrane element <b>2400</b>. The first fluid may pass through each membrane element <b>2400</b> in a similar fashion and may be plumbed through a top plate second fluid port <b>2502</b>. In some examples, the fluid ports of the membrane elements <b>2400</b>, top plate, and/or bottom plate may include interconnects, for example open nipples <b>2801</b> or closed nipples <b>2802</b>.

A top plate third fluid port <b>2503</b> may direct a second fluid to a third fluid port <b>2403</b> of the head plate of a first membrane element <b>2400</b>. The second fluid may then pass through the first membrane element <b>2400</b>. The second fluid may then pass to a second membrane element <b>2400</b> by exiting the first membrane element <b>2400</b> through a fourth fluid port <b>2404</b> located on the foot plate of the first membrane element <b>2400</b>. The fourth fluid port <b>2404</b> may be coupled to the third fluid port <b>2403</b> of a second membrane element <b>2400</b> positioned beneath the first membrane element <b>2400</b>. Similarly, the first fluid may pass through a third membrane element <b>2400</b>. For a parallel configuration, all the third fluid ports <b>2403</b> and fourth fluid ports <b>2404</b> may be on a first side of each membrane element <b>2400</b>. The second fluid may pass through each membrane element <b>2400</b> in a similar fashion and may be plumbed through a top plate fourth fluid port <b>2504</b>.

In one example of a parallel configuration, all fluid ports on a first side of the stack except a bottom fluid port may be fitted with open nipples <b>2801</b>. The bottom fluid port on the first side may be fitted with a closed nipple <b>2802</b>. All fluid ports on a second side of the stack except the top fluid port may be fitted with open nipples <b>2801</b>. The top fluid port on the second side may be fitted with a closed nipple.

<figref idref="DRAWINGS">FIG. <b>21</b>B</figref> is a cross-sectional view of a membrane element <b>2400</b> stacked in series, according to some embodiments. A top plate first fluid port <b>2501</b> may direct a first fluid to a first fluid port <b>2401</b> of the head plate of a first membrane element <b>2400</b>. The first fluid may then pass through the first membrane element <b>2400</b>. The first fluid may then pass to a second membrane element <b>2400</b> by exiting the first membrane element <b>2400</b> through a second fluid port <b>2402</b> located on the foot plate of the first membrane element <b>2400</b>. The second fluid port <b>2402</b> may be coupled to first fluid port <b>2401</b> of a second membrane element <b>2400</b> positioned beneath the first membrane element <b>2400</b>. Similarly, the first fluid may pass through a third membrane element <b>2400</b>. For a series configuration, the first fluid ports <b>2402</b> and second fluid ports <b>2402</b> of each membrane element <b>2400</b> may alternate between a first side and a second side of the membrane element <b>2400</b>. After passing through the membrane element <b>2400</b>, the first fluid may directly exit the last membrane element <b>2400</b> through its second fluid port <b>2402</b>, or may pass through a bottom plate. Alternately, the first fluid may be routed back to the top plate and may flow out through the top plate second fluid port <b>2502</b>.

A top plate third fluid port <b>2503</b> may direct a second fluid to a third fluid port <b>2403</b> of the head plate of a first membrane element <b>2400</b>. The second fluid may then pass through the first membrane element <b>2400</b>. The second fluid may then pass to a second membrane element <b>2400</b> by exiting the first membrane element <b>2400</b> through a fourth fluid port <b>2404</b> located on the foot plate of the first membrane element <b>2400</b>. The fourth fluid port <b>2404</b> may be coupled to the third fluid port <b>2403</b> of a second membrane element <b>2400</b> positioned beneath the first membrane element <b>2400</b>. Similarly, the first fluid may pass through a third membrane element <b>2400</b>. For a series configuration, the third fluid ports <b>2403</b> and fourth fluid ports <b>2404</b> of each membrane element <b>2400</b> may alternate between a first side and a second side of the membrane element <b>2400</b>. After passing through the membrane element <b>2400</b>, the second fluid may directly exit the last membrane element <b>2400</b> through its fourth fluid port <b>2404</b>, or may pass through a bottom plate. Alternately, the second fluid may be routed back to the top plate and may flow out through the top plate fourth fluid port <b>2504</b>.

In one example of a series configuration, the fluid ports on a first side of the stack may alternate between being fitted with open nipples <b>2801</b> and closed nipples <b>2802</b>. Similarly, the fluid ports on a second side of the stack may alternate between being fitted with open nipples <b>2801</b> and closed nipples <b>2802</b>, in which the first and second side may have alternating types of nipples. For example, whenever a fluid port on the first side is fitted with an open nipple <b>2801</b>, the corresponding fluid port on the second side may be fitted with a closed nipple <b>2802</b>.

<figref idref="DRAWINGS">FIG. <b>23</b></figref> is an isometric view of a membrane element <b>2400</b>, according to some embodiments. In some examples, a partially enclosed membrane element <b>2400</b> may be immersed in a first fluid. In this configuration, the one or more openings associated with a first fluid may be exposed, thereby allowing the first fluid to enter and exit the membrane element <b>2400</b>. The membrane element <b>2400</b> may include a first fluid port <b>2401</b> and a second fluid port <b>2402</b> to plumb a second fluid through the membrane element <b>2400</b>. In some examples, the first fluid may be a feed fluid and the second fluid may be a draw fluid. The membrane element <b>2400</b> may be immersed in the feed fluid, allowing the feed fluid to pass through the membrane element <b>2400</b>. The draw fluid may be plumbed through the membrane element <b>2400</b> as described above. Alternatively, the membrane element <b>2400</b> may be immersed in the draw fluid while the feed fluid may be plumbed into the membrane element <b>2400</b> by fluid ports, as described above. It may be advantageous to use this configuration for membrane bioreactors.

<figref idref="DRAWINGS">FIG. <b>24</b></figref> is an isometric view of a skid of membrane elements <b>2400</b>, according to some embodiments. In some examples, many membrane elements <b>2400</b> may be coupled in arrays that may be suitable for operation in a large plant. Arrays may be formed by stacking membrane elements <b>2400</b> together, and creating a fluid interface between the membrane elements <b>2400</b> the array. The fluid interface may be in series, parallel, or combinations thereof. One or more stacks may be combined in a common frame <b>2701</b> to provide rigid endplates and mechanical support. A top fluid interface <b>2702</b> and a bottom fluid interface <b>2703</b> may provide a fluid interface between different stacks, thereby providing a fluid interface for the entire array. In addition, skids including multiple arrays may be provided. The skid may be a standalone module, and may provide pumps for one or more fluids and controls to run efficiently. Additionally, leak detection may be included at the skid level. The skid may have headers that may couple each array in parallel. Modules may be isolated and removed from the skid for maintenance. In some examples, many skids may be used to operate a large plant.

Examples of membranes, elements, modules, and/or stacks described herein may generally be used to perform forward osmosis. Forward osmosis generally refers to a process whereby a solute in a draw solution is greater than a solute in a feed solution. Water traverses the forward osmosis membrane, generally from the feed to the draw solution, decreasing the concentration of solute in the draw. Any number of solutes may be manipulated using membranes, devices, and systems described herein including, but not limited to salts. Any number of fluids may be used to implement the feed and draw fluids, including, but not limited to, water, industrial waste, commercial waste, agricultural waste, and beverages. Pressure retarded osmosis generally refers to a process whereby energy or pressure is generated by fluid transport driven by the osmotic pressure difference between a feed solution and a draw solution. The feed solution may be wastewater or river water and the draw solution may be seawater or reverse osmosis brine. Membrane distillation generally refers to a process whereby fluid from a liquid feed solution at a high temperature passes through a membrane as vapor and condenses to a permeate solution at a lower temperature. The feed may be waste water, seawater, or any solution of high salt concentration.

Example Performance

Example performance metrics achieved using examples of membrane plate assemblies described herein are provided below. The example metrics are provided by way of example and to facilitate an understanding of example performance achievable using assemblies described herein. The examples provided are not the only performance metrics achievable, and not all embodiments may achieve the described performance

<tables id="TABLE-US-00001" num="00001"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217pt" align="center" /><thead><row><entry namest="1" nameend="1" rowsep="1">TABLE 1</entry></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row><row><entry>Performance of Porifera's Gen 1 membrane plate assembly.</entry></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row>&lt;entry /&gt;</row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="3"><colspec colname="1" colwidth="126pt" align="left" /><colspec colname="2" colwidth="49pt" align="right" /><colspec colname="3" colwidth="42pt" align="left" /><tbody valign="top"><row><entry>Membrane area per element</entry><entry>7.0</entry><entry>m2</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="1" colwidth="126pt" align="left" /><colspec colname="2" colwidth="91pt" align="center" /><tbody valign="top"><row><entry>Membrane Type</entry><entry>Forward osmosis</entry></row><row><entry>Operational pH limits</entry><entry>2-11</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="3"><colspec colname="1" colwidth="126pt" align="left" /><colspec colname="2" colwidth="49pt" align="right" /><colspec colname="3" colwidth="42pt" align="left" /><tbody valign="top"><row><entry>Water processed by element with 5.5 wt %</entry><entry>190-240</entry><entry>L/h</entry></row><row><entry>NaCl draw vs. water (FO mode)</entry></row><row><entry>Reverse salt flux of element</entry><entry>0.2-0.6</entry><entry>g/L</entry></row><row><entry>Water processed by element with 5.5 wt %</entry><entry>65-75</entry><entry>L/h</entry></row><row><entry>NaCl draw vs. 3.25% NaCl (FO mode)</entry></row><row><entry>Feed spacer</entry><entry>0.030″</entry><entry>Fishnet</entry></row><row><entry>Head loss</entry><entry>0.03</entry><entry>psi/gpm</entry></row><row><entry>Element volume, including housing</entry><entry>0.03</entry><entry>m3</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="1" colwidth="126pt" align="left" /><colspec colname="2" colwidth="91pt" align="center" /><tbody valign="top"><row><entry>Physical dimensions</entry><entry>16″ × 18″ × 7″</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="3"><colspec colname="1" colwidth="126pt" align="left" /><colspec colname="2" colwidth="49pt" align="right" /><colspec colname="3" colwidth="42pt" align="left" /><tbody valign="top"><row><entry>Weight (wet)</entry><entry>72</entry><entry>lbs</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="1" colwidth="126pt" align="left" /><colspec colname="2" colwidth="91pt" align="center" /><tbody valign="top"><row><entry>Materials</entry><entry>Plastic &amp; Aluminum</entry></row><row><entry>Plumbing Interface</entry><entry>Porifera Quick Change</entry></row><row>&lt;entry /&gt;<entry>Manifold</entry></row><row><entry namest="1" nameend="2" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

<tables id="TABLE-US-00002" num="00002"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217pt" align="center" /><thead><row><entry namest="1" nameend="1" rowsep="1">TABLE 2</entry></row></thead><tbody valign="top"><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row><row><entry>Performance of Porifera's Gen 1 membrane</entry></row><row><entry>plate assembly in FO mode with different flow</entry></row><row><entry>rates using 300 TDS Feed and 1M NaCl Draw.</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="6"><colspec colname="1" colwidth="42pt" align="center" /><colspec colname="2" colwidth="42pt" align="center" /><colspec colname="3" colwidth="35pt" align="center" /><colspec colname="4" colwidth="21pt" align="center" /><colspec colname="5" colwidth="42pt" align="center" /><colspec colname="6" colwidth="35pt" align="center" /><tbody valign="top"><row><entry>Draw</entry><entry>Feed</entry><entry>Flux at</entry>&lt;entry /&gt;<entry>Draw</entry><entry>Feed</entry></row><row><entry>Flow rates</entry><entry>Flow rates</entry><entry>25 C.</entry><entry>RSF</entry><entry>Head Loss</entry><entry>Head Loss</entry></row><row><entry>(gpm)</entry><entry>(gpm)</entry><entry>(LMH)</entry><entry>(g/L)</entry><entry>(psi)</entry><entry>(psi)</entry></row><row><entry namest="1" nameend="6" align="center" rowsep="1" /></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="6"><colspec colname="1" colwidth="42pt" align="char" char="." /><colspec colname="2" colwidth="42pt" align="char" char="." /><colspec colname="3" colwidth="35pt" align="char" char="." /><colspec colname="4" colwidth="21pt" align="char" char="." /><colspec colname="5" colwidth="42pt" align="char" char="." /><colspec colname="6" colwidth="35pt" align="char" char="." /><tbody valign="top"><row><entry>2.0</entry><entry>2.0</entry><entry>21.9</entry><entry>0.46</entry><entry>0</entry><entry>0.9</entry></row><row><entry>4.0</entry><entry>4.0</entry><entry>25.3</entry><entry>0.39</entry><entry>0</entry><entry>1.2</entry></row><row><entry>6.0</entry><entry>6.0</entry><entry>26.7</entry><entry>0.39</entry><entry>0.3</entry><entry>1.5</entry></row><row><entry>8.0</entry><entry>8.0</entry><entry>27.3</entry><entry>0.31</entry><entry>0.7</entry><entry>2.1</entry></row><row><entry>10.0</entry><entry>10.0</entry><entry>28.0</entry><entry>0.35</entry><entry>1.2</entry><entry>2.1</entry></row><row><entry namest="1" nameend="6" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

<tables id="TABLE-US-00003" num="00003"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217pt" align="center" /><thead><row><entry namest="1" nameend="1" rowsep="1">TABLE 3</entry></row></thead><tbody valign="top"><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row><row><entry>Packing Density of Porifera's Elements</entry></row><row><entry>compared to commercial RO and FO elements.</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="4"><colspec colname="offset" colwidth="14pt" align="left" /><colspec colname="1" colwidth="98pt" align="left" /><colspec colname="2" colwidth="28pt" align="center" /><colspec colname="3" colwidth="77pt" align="center" /><tbody valign="top"><row>&lt;entry /&gt;&lt;entry /&gt;<entry>Area</entry><entry>Packing Density</entry></row><row>&lt;entry /&gt;<entry>Element</entry><entry>(m²)</entry><entry>(m²/m³)</entry></row><row>&lt;entry /&gt;<entry namest="offset" nameend="3" align="center" rowsep="1" /></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="4"><colspec colname="offset" colwidth="14pt" align="left" /><colspec colname="1" colwidth="98pt" align="left" /><colspec colname="2" colwidth="28pt" align="char" char="." /><colspec colname="3" colwidth="77pt" align="char" char="." /><tbody valign="top"><row>&lt;entry /&gt;<entry>RO 4040 7 m²</entry><entry>7</entry><entry>263.7</entry></row><row>&lt;entry /&gt;<entry>RO 8040 - 41 m²</entry><entry>41</entry><entry>569.2</entry></row><row>&lt;entry /&gt;<entry>Porifera's Gen 2 - 80 m²</entry><entry>80</entry><entry>615.0</entry></row><row>&lt;entry /&gt;<entry>Porifera's Gen 1 - 7 m²</entry><entry>7</entry><entry>233.0</entry></row><row>&lt;entry /&gt;<entry>Commercial FO 8040 - 17 m²</entry><entry>17</entry><entry>236.0</entry></row><row>&lt;entry /&gt;<entry>Commercial FO 4040 - 3 m²</entry><entry>3</entry><entry>113.0</entry></row><row>&lt;entry /&gt;<entry>Commercial FO 4040 - 1.2 m²</entry><entry>1.20</entry><entry>45.2</entry></row><row>&lt;entry /&gt;<entry namest="offset" nameend="3" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention.